1. Field of the Invention
The present invention relates to an exercise apparatus and, more particularly, to an adjustable exercise apparatus that can be used for a multitude of exercises.
2. Description of Related Art
Many exercise devices have been developed of a “weight type” in which weights provide resistance to the exertion of muscular force. Such machines commonly employ weight stacks that allow a user to vary the weight lifted during the exercise. U.S. Pat. Nos. 6,447,430, 5,776,040, and 4,500,089 are examples of such machines.
Weight stack machines often, in normal use, do not provide a consistent resistance. A weight lifter normally thinks that 100 pounds of weight will provide 100 pounds of resistance throughout the exercise stroke; however, this is true only if the weight is moved at a slow and generally constant speed. If the weight lifter quickly moves the weight, the changes in speed of movement will cause the weight to change. Accordingly, manufacturers of weight stack machines commonly instruct those training on their machines to train at a speed of out on two seconds and back on four seconds, thus keeping the speed slow enough to make the acceleration forces insignificant. However, if a user accelerates the weight during the exercise stroke, the resistance force will change.
Pneumatic exercise equipment has been developed in response to this shortcoming of weight stacks. Such exercise equipment simulates the desired characteristics of a weight stack exercise machine by easily permitting the weight lifter to increase or decrease the resistance; however, pneumatic exercise equipment also permits the weight lifter to increase speed without the resistance changing because such machines do not have a significant inertia of motion. Consequently, pneumatic exercise equipment ensures full muscular effort throughout the stroke.
Pneumatic exercise equipment commonly include a pneumatic cylinder with a piston rod that moves linearly. A piston divides the cylinder into two chambers. The rod is connected to the piston and extends through one of the chambers. The piston rod also is usually operatively connected to a handle or other user interface. As the user pushes (or pulls, depending upon which cylinder chamber is pressurized) on the handle, movement of the rod is resisted by air within the cylinder. This resistance to further movement provides exercise resistance.
Over the stroke of the rod within the cylinder, it can be expected that the resistance provided by the cylinder will increase as the rod is progressively pushed into the cylinder. To make this increase less dramatic, an air reservoir, also known as an accumulator, can be coupled with the cylinder through an air line. The air line allows air to flow between the cylinder and the accumulator and thus equalizes the air pressure between these components.
The user can choose a preset resistance force by controlling the air pressure within the cylinder/accumulator assembly. A source of compressed air communicates with the accumulator through an air supply line. An air addition valve, a pressure gauge, and a bleed-off valve are interposed in the line. The pressure gauge preferably is configured to display the resistance force anticipated for the user rather than the actual air pressure within the system. To adjust the resistance force to a desired level, the user adds or removes air from the pneumatic system. Air is added by actuating the air addition valve. Air is removed by actuating the bleed-off valve. U.S. Pat. No. 4,257,593 discloses an example of a pneumatic exercise device.
Due to the nature of pneumatics, the resistance curve produced for a given air pressure as the piston rod is moves from an initial position to a fully retracted position (or fully extended position if pulled) remains substantially the same even though the speed at which the piston rod moves may vary. The resistance, however, will increase during the exercise stroke as the air compresses under the exerted force of the user.